The need for soil retaining and erosion control structures must surely date back to the earliest stages of civilization. Man first sought camp sites along streams, rivers and shore lines and later settled in such areas, so that some of his earliest permanent structures were undoubtedly subject to soil instability problems. In all likelihood, the first soil retaining effort involved placement of irregular rocks as a protective blanket at some exposed location to discourage erosion. This evolved into the more formalized application of riprap well known in the art. Gabions, wherein relatively small rock pieces are packed into building block-like containers made of wire netting, are a variation which have been used in gravity wall and blanket type erosion control structures for many years.
Gabions have also come to be used for retaining walls. In a typical application, the soil bank to be protected is cut back to allow space for a wide based, upwardly tapering stack of tiers of gabions. Adjacent gabions are usually wired together to act as a continuous barrier and the gabions of alternating tiers may be staggered to promote an interlocking effect. Gabions have an economic advantage over precast or monolithic concrete construction in that heavy equipment and skilled labor are not essential to their installation. The rock pieces used to fill them may weigh no more than about 25 pounds apiece and are a relatively inexpensive material. Thus, the gabions, which are themselves lightweight, wire net structures in the form of cubes or rectangular prisms of up no three or four feet on a side, may be set in place and filled by hand or light machinery. Moreover, the open interstices of a gabion structure provide far better drainage than is possible with concrete or masonry construction, where French drain arrangements must usually be provided to avoid entrapment of water and potentially damaging hydraulic forces.
An engineering analysis identifies the essential design criteria of retaining structures as:
A. Adequate bearing support for the structure. PA1 B. Resistance to overturning forces. PA1 C. Resistance to sliding forces.
Contemporary retaining and erosion control structures, designed according to accepted practice, utilize interlocking, precast panels or monolithic systems, held in place by various methods. Gabion based structures of the prior art, which resist soil displacement and overturning forces by virtue of sheer mass and wide footprint, have been considered to be technically inferior to the structures of current design practice. As a result, gabion structures have mainly been used only in less demanding applications.
The object of the present invention is therefore, to provide gabion based retaining structures which are technically equal or superior to current design practice and furthermore, to achieve this improved structure while retaining the inherent advantages of gabions. A further object is to provide this improved structure at lower cost than for a comparable conventional gabion structure.
The present invention achieves this object by introducing a unitary beam into single row tiers of the gabion structure and anchoring this unitary beam so as to react the soil retention loads imposed on the gabion tiers into a stable adjacent formation or structure. The anchors balance the single row tiers against soil pressure so that a multiple row wide base is not required to resist overturning forces and great mass is not needed to resist sliding forces.